JP3539524B2 - Semiconductor laser drive circuit - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a semiconductor laser drive circuit used for an optical disk device or the like.
[0002]
[Prior art]
2. Description of the Related Art In an optical disk device, when writing data to a disk, a laser beam focused by a pickup is irradiated onto a rotating disk surface, and the laser beam is intensity-modulated at high speed to record a mark. A semiconductor laser is generally used as a laser light source. There are two types of semiconductor lasers, one with the cathode side grounded and the other with the anode side grounded. FIG. 5 shows an example of a conventional drive circuit for a semiconductor laser in which the cathode side is grounded. In this figure, a semiconductor laser 107 is driven in parallel by a bias current source 103 composed of a PNP transistor 101 and a resistor 102, and a peak current source 106 also composed of a PNP transistor 104 and a resistor 105. Side current is switched by the PNP transistor 108. The control of the peak light output is set by the base voltage of the transistor 104 of the peak current source 106, and the control of the bias light output is similarly set by the base voltage of the transistor 101 of the bias current source 103. As the transistors 101, 104, and 108 used here, a PNP transistor is generally used from the relationship between the polarity of the semiconductor laser 107 and the positive power supply.
[0003]
[Problems to be solved by the invention]
For the purpose of writing data to an optical disk at a high speed, naturally, the transistor that performs the switching described above also requires a high-speed response. The conventional laser drive circuit described uses a PNP transistor. The PNP transistor is inferior in the characteristics of a large current and high-speed operation to the structure as compared with the NPN transistor. In order to obtain sufficient characteristics with a PNP transistor, there is a problem that a special manufacturing process is required, resulting in an expensive component. As another problem, since the control voltage for setting the laser output is based on the power supply voltage, when the power supply voltage fluctuates, the control voltage relatively changes and the laser output also fluctuates. I was
[0004]
The present invention has been made to solve the above-described problems, and provides a semiconductor laser driving circuit which enables high-speed operation using only an NPN type transistor as a driving circuit transistor and is not affected by fluctuations in power supply voltage. Aim.
[0005]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided a first NPN transistor having a collector connected to a positive power supply and an emitter connected to one end of a first resistor, and an anode connected to the other end of the first resistor. A semiconductor laser whose cathode is grounded to ground; a second NPN transistor whose collector is connected to the anode of the semiconductor laser and whose emitter is grounded via a second resistor to ground; A logic buffer supplied to an end of the semiconductor laser and supplying a plurality of outputs to the base of the second NPN transistor via a resistor together with a first power of the semiconductor laser at a base voltage of the first NPN transistor. Controlling the second power by the power supply voltage of the logic buffer, thereby causing the semiconductor laser to emit the first pulse by the plurality of input data. It is characterized in that the switching to the multi-value between over and the second power.
[0007]
Thus, according to the invention, the first NPN transistor supplies the current required by the semiconductor laser for the first power output. The second NPN transistor driven at high speed by the logic buffer to which the data is input shunts the current and reduces the current of the semiconductor laser . Since a multi-bit logic buffer is used, a multi-level optical output between the first power and the second power can be obtained. The setting of the output power is controlled by the base voltage of the first NPN transistor and the power supply voltage of the logic buffer, respectively, and both are determined by the reference voltage from the grounding point.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
(1st Embodiment)
FIG. 1 is a circuit diagram of a semiconductor laser drive circuit described as a first embodiment of the present invention. In FIG. 1, a first NPN transistor 1 has a collector connected to a power supply and an emitter connected to one end of a first resistor 2. The other end of the first resistor 2 is connected to the collector of the second transistor 4 and the anode terminal of the semiconductor laser 3. The cathode end of the semiconductor laser 3 is grounded, and the emitter of the transistor 4 is grounded via the second resistor 5. The logic buffer 6 is connected to the base of the second transistor 4. A data input terminal 7 is connected to an input terminal of the logic buffer 6, a second power setting input terminal 9 is connected to a power terminal thereof, and a first power setting terminal is connected to a base of the first transistor 1. The input terminal 8 is connected. The semiconductor laser 3 is of a positive drive type with a cathode grounded.
[0010]
FIG. 2 is a signal waveform diagram showing the operation of the present embodiment. The operation of the present embodiment will be described with reference to FIGS. First, when the voltage of the first power setting voltage input terminal 8 is increased to the first power setting voltage in a state where the second NPN transistor 4 is cut off (period a in FIG. 2), the first NPN transistor 4 is turned off. 1 is in operation. Therefore, a current required for the first power is supplied to the semiconductor laser 3 via the first resistor 2, and the semiconductor laser 3 emits light at the first power. Next, when the data input terminal 7 is set high and the voltage of the second power setting voltage input terminal 9, that is, the power supply voltage of the logic buffer 6 is raised to the second power setting voltage (period b in FIG. 2), the logic buffer 6, the base voltage of the second NPN transistor 4 rises, and the second NPN transistor 4 is activated. Since the second NPN transistor 4 is grounded by the second resistor 5 and is in a parallel circuit with the semiconductor laser 3, it functions to reduce the current of the semiconductor laser 3, and the semiconductor laser 3 emits light at the second power. I do. Further, when the input data is switched in this state (period c in FIG. 2), the output of the semiconductor laser 3 is switched between the first power and the second power.
[0011]
Although the present embodiment has a very simple configuration, it uses an NPN transistor and a logic buffer, so that it is inexpensive and has high-speed performance. Further, since the control voltage for determining the power is based on the ground point, the output of the laser does not change even if the power supply voltage slightly changes.
[0012]
(2nd Embodiment)
FIG. 3 is a circuit diagram of a semiconductor laser drive circuit described as a second embodiment of the present invention. In FIG. 3, components having the same reference numerals as those in the first embodiment have the same functions, and a description thereof will be omitted. In this figure, an A data input terminal 11 and a B data input terminal 12 are connected to a 2-bit logic buffer 10, and the logic buffer 10 outputs these outputs via a third resistor 13 and a fourth resistor 14. To the base of the second transistor 4. The power supply terminal of the logic buffer 10 is connected to the second power setting input terminal 9.
[0013]
FIG. 4 is a signal waveform diagram showing the operation of the present embodiment. The operation of the present embodiment will be described with reference to FIGS. The description of the operation in common with the first embodiment is omitted. First, similarly to the first embodiment, the semiconductor laser 3 emits light at the first power (period a in FIG. 4). Next, the A data input terminal 11 and the B data input terminal 12 are both set to high, the power supply voltage of the logic buffer 10 is raised to the second power setting voltage (period b in FIG. 4), and the current of the semiconductor laser 3 is reduced. , And emit light at the second power. Further, in this state, A data and B data are switched (period c in FIG. 4). Here, when both the A data and the B data are high, the voltage synthesized by the third resistor and the fourth resistor is the highest, the second NPN transistor 4 passes the current most, and the semiconductor laser 3 Light is emitted at the second power because the current is reduced most. When both the A data and the B data are low, on the contrary, the current of the semiconductor laser 3 increases most and emits light at the first power. Further, when either one of the A data and the B data is high, light is emitted at an intermediate value between the first power and the second power. When the A data and the B data are input as in the period c in FIG. 4, the laser output can be modulated in four stages from the first power to the second power.
[0014]
In the second embodiment, the case where the data input is 2 bits is shown. However, it is apparent that the control of four values or more is possible if the data input is three bits or more.
[0015]
【The invention's effect】
Although the semiconductor laser drive circuit of the present invention has a simple configuration using NPN-type transistors that are relatively inexpensive and have good characteristics compared to PNP-type transistors and general logic buffers, the semiconductor laser drive circuit of the present invention uses This has the effect of ensuring high speed and stability against fluctuations in power supply voltage. Therefore, when combined with an automatic laser power control circuit for feedback control, it is most suitable as a laser driving means for an optical disk device.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a semiconductor laser drive circuit according to a first embodiment of the present invention.
FIG. 2 is a signal waveform diagram showing an operation of the first embodiment.
FIG. 3 is a circuit diagram of a semiconductor laser drive circuit according to a second embodiment of the present invention.
FIG. 4 is a signal waveform diagram showing an operation of the second embodiment.
FIG. 5 shows a conventional semiconductor laser drive circuit.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 First NPN transistor 2, 5, 13, 14 Resistor 3 Semiconductor laser 4 Second NPN transistor 6, 10 Logic buffer 7 Data input terminal 8 First power setting input terminal 9 Second power setting input terminal 11 A data Input terminal 12 B data input terminal

Claims (1)

A first NPN transistor having a collector connected to a positive power supply and an emitter connected to one end of the first resistor; and a semiconductor laser having an anode connected to the other end of the first resistor and a cathode grounded to ground. A second NPN transistor having a collector connected to the anode of the semiconductor laser and an emitter grounded to the ground via a second resistor, and a plurality of input data supplied to an input terminal; A logic buffer for supplying an output to the base of the second NPN transistor via a resistor,
The first power of the semiconductor laser is controlled by the base voltage of the first NPN transistor, and the second power is controlled by the power supply voltage of the logic buffer, so that the semiconductor laser is controlled by the plurality of input data. A semiconductor laser drive circuit, which switches between two power levels.

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